Can't move it? Afraid it will be flooded? Then bag it.
Big tarp. A real one; heavy waterproof canvas.
Figure out where you want the vehicle to be placed. Plan for your anchors(!) (Yes, anchors; if it floods, the vehicle is going to float, so plan accordingly.)
Lay out your tarp. Roll the vehilce ONTO the tarp. Then wrap it up.
Be careful with the corners; close the tarp like a Christmas package, bringing the open end of the corner-folds UP. Us lots of line (rope, for non-sailors). You want the tarp lashed fast to itself, so as to form the bag, and once bagged, lashed to the vehicle so the open ends of the tarp will stay well above the line of the windows. (If the flooding is deep enough, the vehicle will float when the water gets about to the tops of the hub cabs. With regard to your anchors, make sure you take the anticipated DEPTH of flooding into account. Properly moored, the bagged vehicle will rise WITH the waters, settle back down as they receed.)
Last step is to lash another, smaller tarp over the folded, lashed, open-end of the first, so as to form a 'sky' or roof that will shed rain.
Does it work? Damn betcha. (This method is how you get your vehicle across rivers too deep to ford.)
I thought everyone knew about bagging your bug (or at least, all old sailors). Recently I've gotten a couple of woeful messages from VW owners who obviously did NOT know how to protect their project from flooding.
Now you know. Good luck with it.
-Bob Hoover